The invention relates to a circuit configuration for voltage stabilization.
The operation of electronic circuits generally requires one or two DC voltages. The DC voltages are almost always obtained directly from the AC mains voltage by using power supply circuits. In the simplest case, the power supply circuits include a mains transformer, a rectifier and a filter circuit. However, nowadays, switched-mode power supplies are increasingly being used within the power supply circuits in order to reduce power supply losses. However, the operation of the electronic circuit requires that the DC voltage supplied by the power supply or the switched-mode power supply complies with a required voltage value as precisely as possible. However, in clocked circuit configurations in power electronics, voltage fluctuations can arise on the connection lines between the mains connection and the load connection. The voltage fluctuations are caused by mains voltage fluctuations, temperature fluctuations and load current fluctuations. Such voltage fluctuations are undesirable since they result in increased EMC emissions requiring radio interference suppressions, an increased power loss, excitation of the surroundings, and instabilities of the entire circuit configuration.
However, despite these voltage fluctuations, the DC voltage necessary for operating the electronic circuit should be constant to the greatest possible extent within a certain tolerance, for example between 0.5 and 5%. For these reasons, the output voltage of the rectifier circuits arranged within the power supply circuits is not directly suitable as an operating voltage for an electronic circuit, but rather must be stabilized and smoothed by a circuit configuration for voltage stabilization connected downstream.
In the simplest case, such a voltage stabilization circuit is produced from a linear voltage regulator which is connected downstream of the mains transformer and the rectifier and which may replace a filter circuit, for example. Such voltage regulators suppress the input voltage fluctuations and correct load current fluctuations that possibly occur. In the case of a switched-mode power supply, the customary mains transformer is dispensed with, as is known. The mains voltage is rectified directly in this case and this DC voltage is brought to the desired output voltage and stabilized by a DC voltage converter or a switching regulator.
Such circuits for voltage realization are known in many cases and are described, for example, in R. Kxc3x6stner, A. Mxc3x6schwitzer, xe2x80x9cElektronische Schaltungenxe2x80x9d [xe2x80x9cElectronic circuitsxe2x80x9d], Karl-Hanser-Verlag, 1993, in particular on pages 264 to 286.
These simple circuits for voltage stabilization which are realized by a voltage regulator or by the functionality of the switched-mode power supply itself for the most part do not satisfy, or do not satisfy well enough, the requirements which have to be made of a circuit for voltage stabilization. Therefore, in addition or as an alternative to the voltage regulators, passive or active filters for active compensation of the voltage fluctuations are also often found in clocked circuits of power electronics. Although good voltage stabilization can in many cases be achieved with active filtering, the outlay for such a voltage stabilizer is often so great that it is not realized for economic reasons.
All of the abovementioned circuits for voltage stabilization have the inherent disadvantage that they are arranged at least partially directly in the respective output line on which an interference level to be compensated runs, in order thus to ensure dynamic correction or compensation of the interference signal. As a result, however, the stabilization circuit is no longer free of perturbations since the components of the circuit for voltage stabilization which are arranged in the load path always also have an influence on the signal to be stabilized.
The article xe2x80x9cDesign and Evaluation of an Active Ripple Filter with Rogowski-Coil Current Sensingxe2x80x9d, by M. Zhu et al. of the Massachusetts Institute of Technology describes an active filter for voltage stabilization, which does not have the described disadvantage. In this case, an inductive measurement pick-up for detecting the interference signal is provided. A compensation signal is generated from the interference signal, which compensation signal is fed in inductively. The direct electrical isolation of the circuit configuration for voltage stabilization from the corresponding connection lines with the interference signal avoids a direct coupling and thus a direct perturbation of the circuit for voltage stabilization on the load circuit. However, the bandwidth of the circuit for voltage stabilization is limited on account of the direct electrical isolation with a ferrite. Furthermore, a high system loading exists due to the current measurement and the increased power consumption as a result of this. This can be eliminated only through a disproportionately high outlay on circuitry. If this is not done, then a slight temporal offset exists at the measurement frequency. Therefore, such a circuit for voltage stabilization is suitable only for relatively low frequencies in the range up to 125 kHz.
In many cases, however, it is necessary also to correct interference levels with higher frequencies. Such higher-frequency interference frequencies become apparent particularly seriously if they are in the frequency band of the radio frequencies, i.e. in the range of about 1 MHz and above, since an interfering noise is thereby superposed on the radio reception, which should understandably be avoided particularly in the case of automotive applications.
It is accordingly an object of the invention to provide a circuit configuration for voltage stabilization which overcomes the above-mentioned disadvantages of the prior art apparatus of this general type.
In particular, it is an object of the invention to provide a circuit configuration for voltage stabilization which stabilizes an output signal superposed with an interference level on an output line as much as possible in a manner free of perturbations.
With the foregoing and other objects in view there is provided, in accordance with the invention, a voltage stabilization circuit configured between two signal lines each carrying a respective signal. An interference signal is superposed on the signal of at least one of the signal lines. The voltage stabilization circuit has an amplifier circuit that obtains a difference between a signal derived from the interference signal and a reference signal, amplifies the difference and generates an antiphase signal having a phase that is opposite that of the interference signal. The voltage stabilization circuit has a matching circuit for potential matching connected downstream of the amplifier circuit. The matching circuit generates a compensation signal from the antiphase signal. The compensation signal is superposed on the signal on which the interference potential is superposed.
The voltage stabilization circuit enables dynamic and perturbation-free compensation of an interference level by using an active compensation circuit which detects the interference level as a difference with respect to a freely settable reference signal, amplifies it using a differential amplifier and feeds it in antiphase onto the connection line or lines superposed with the interference level in the form of a compensation current or a compensation voltage. In this case, the voltage stabilization circuit only taps off the interference signal or the signal on the connection line affected by interference and superposes a compensation signal on the connection line affected by interference. Otherwise, however, the load circuit remains unaffected by the stabilization circuit. The voltage stabilization circuit advantageously has no components in the signal path of the connection line affected by interference. The result is that the stabilization circuit does not cause perturbations on the connection line. The dynamic range and the frequency range of the stabilization circuit in which the circuit according to the invention operates optimally can be achieved by suitably dimensioning the stabilization circuitxe2x80x94that is to say of the differential amplifier, the matching circuit, the measurement circuit, the technology, the transition frequency, the supply voltage.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a circuit configuration for voltage stabilization, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.